The Snap to Market (SNAP MKT) order is similar to a pegged order, as the original order price is determined by the current bid/ask plus or minus an offset. But unlike the pegged order price, the "snap to" order price doesn't continue to peg as the price moves.
A Snap to Market BUY order snaps to the ask minus the offset, to set the order price. For a SELL order, it snaps to the bid plus the offset.
To create a Snap to Market order
Create a buy or sell order.
From the Type field select SNAP MKT.
Specify an offset amount that will be subtracted from the bid (for a buy order) to determine the limit price.